The present invention relates generally to the field of labyrinth seals. In particular, the present invention relates to damping devices for stationary labyrinth seals.
Labyrinth seals are common annular devices used in turbomachinery systems such as jet engines and turbopumps. The labyrinth seals are positioned within the system to control leakages between different cavities of the system. By minimizing leakages within the system, desired pressure drops and flow rates can be maintained, resulting in optimum performance of the system. Typically, a labyrinth seal includes a rotating component running in close proximity to a stationary component. Either the rotating component or the stationary component may include the labyrinth seal having a plurality of teeth. The individual teeth of the labyrinth seal are spaced at predetermined distances from each other along the component to throttle down the pressure of the system by a desired amount.
Labyrinth seals are often subjected to severe, vibratory environments. The vibrations may cause cracking, resulting in high cycle fatigue (HCF) failures of the labyrinth seals. The cracking may be attributed to various dynamic excitation sources, including, but not limited to: mechanical resonance due to flow path drivers or rotor dynamics, acoustic resonance caused when natural frequencies of fluid-filled cavities coincide with structural frequencies and mode shapes, and aeroelastic instability or flutter. Flutter occurs when the mechanical deflections of the labyrinth seal cause unsteady pressure loads that add energy to the labyrinth seal during vibration in an amount greater than that dissipated by the available damping in the system.
Two approaches are commonly used to prevent HCF failures: (1) modifications to the structure of the labyrinth seal to change the structural dynamic characteristics of the labyrinth seal, such as the natural frequencies and associated mode shapes of the labyrinth seal; and (2) adding mechanical damping devices to dissipate excessive vibratory energies resulting from a resonant condition or flutter instability of the seal. Combinations of (1) and (2) are also used. In the field of damping devices, split-ring dampers are commonly used in conjunction with rotating labyrinth seals. Split-ring dampers rely on the centrifugal field to provide a contact force between the damper and the seal. Energy is dissipated by the friction hysteresis cycle when the amplitude of vibration results in an elastic force in excess of the friction force.
While effective in rotating labyrinth seals, incorporating a split-ring damper in stationary labyrinth seals has proven more challenging due to the absence of centrifugal loading in stationary labyrinth seals. It would thus be beneficial to develop a damping device for use in stationary labyrinth seals.